Coating equipment is one of the crucial process equipment in the display manufacturing industry. A nozzle is the most important and precise component of the coating equipment, and is used for coating a photoresist liquid on the surface of a substrate to form a uniform photoresist film. During the coating process, a foreign object (such as glass chips, a coagulum of dropped photoresist liquid, or the like) often exists on the surface of a platform of the coating equipment or the substrate, and the foreign object may collide with the nozzle and damage the tip of the nozzle when the height of the foreign object exceeds a coating height.
An existing foreign detecting device generally detects the foreign object by using a laser sensor to perform point-line scanning. FIG. 1 is a top view of an existing foreign object detecting device (the hollow arrow in the figure indicates the coating direction). As shown in FIG. 1, a substrate 101 is placed on a platform 102, a nozzle 103 is disposed above the substrate 101, and a laser sensor, which includes a laser transmitter 104 and a laser receiver 105, is provided in front of the nozzle 103 in the coating direction. When a foreign object 106 is present on the substrate 101, as shown in FIGS. 2a and 2b (the hollow arrow in the figure indicates the laser direction), the laser emitted from the laser transmitter 104 is blocked by the foreign object, then the laser receiver 105 receives the laser with weakened intensity, and thus the presence of the foreign object 106 is detected.
However, the above detecting method has the following shortcomings: first, in the case of a foreign object 106 under the substrate 101, as shown in FIGS. 3a and 3b (the hollow arrow in the figure indicates the laser direction), since it is the elevated substrate 101 that is directly scanned, the laser can still arrive at the laser receiver 105, and as a result, the detection sensitivity is unsatisfactory, the foreign object 106 cannot be detected effectively, and the elevated substrate 101 collides with the nozzle 103 to cause greater damage; in addition, the point-line scanning can determine the position of the foreign object 106 in the coating direction (i.e., X direction as shown in FIG. 1) only, but cannot determine the position of the foreign object 106 in the Y direction as shown in FIG. 1, so it is difficult to quickly obtain the specific position of the foreign object 106.